1. Field of the Invention
The present invention relates to a control device for an internal combustion engine which controls a fuel, ignition, valve timing of at least one of an intake valve and an exhaust valve, and so on.
2. Discussion of Background
A conventional technique is disclosed in, for example, JP-A-7-180565. It discloses a means for detecting a cam angle with respect to a crank angle to identify cylinders based on a signal of the cam angle and to detect the cam angle, i.e. valve timing.
FIG. 5 illustrates a structure of a device according to the conventional technique.
Numerical reference 1 designates an internal combustion engine. Numerical reference 2 designates an air cleaner for purifying an air taken in by the internal combustion engine 1. Numerical reference 3 designates an air flow sensor, which measures the amount of the air taken in by the internal combustion engine 1. Numerical reference 4 designates a throttle valve, which adjusts the amount of the air taken in and controls an output of the internal combustion engine 1. Numerical reference 5 designates a throttle sensor, which detects an opening degree of the throttle valve. Numerical reference 6 designates an intake pipe. Numerical reference 7 designates an injector for supplying a fuel in conformity with the amount of the taken air. Numerical reference 8 designates an ignition plug for generating a spark, which burns a mixed air in a combustion chamber of the internal combustion engine 1. Numerical reference 9 designates an exhaust pipe, which exhausts a burned exhaust gas. Numerical reference 10 designates an O.sub.2 sensor, which detects the amount-of remaining oxygen in the exhaust gas. Numerical reference 11 designates a catalytic converter rhodium (CCRO), which can simultaneously purify THC, CO, and No.sub.x, being a noxious gas in the exhaust gas.
Numerical reference 12 designates a sensor plate for detecting the crank angle, which is attached to a crank shaft and is integrally rotated along with the crank shaft. Numerical reference 13 designates a crank angle sensor for detecting a position of the crank shaft, which crank angle sensor generates a signal when a protrusion (not shown) of the sensor plate 12 passes through the crank angle sensor 13 to detect the crank angle. Numerical reference 14 designates a sensor plate for detecting the cam angle; and numerical reference 15 designates a cam angle sensor, which generates a signal when a protrusion (not shown) of the sensor plate 14 passes through the cam angle sensor 15 to detect the cam angle in a similar manner to that in the crank angle sensor. Numerical reference 16 designates an oil control valve for controlling a phase of a cam shaft with respect to the crank shaft by switching an oil pressure to an actuator for varying a cam phase (not shown), which oil control valve is attached to the cam shaft. Numerical reference 17 designates an engine control unit (hereinbelow, referred to as ECU), which controls the phase of the cam shaft with respect to the crank shaft and also controls the fuel and the ignition of the internal combustion engine 1. Numerical reference 18 designates an ignition coil.
An operation of the conventional device will be described with reference to FIG. 6.
An output from the crank angle sensor 13 is formed such that a raise and drop occur at a predetermined position of the crank angle to enable detection of the crank angle. The cam angle sensor 15 is provided such that a signal is generated at a predetermined crank angle. However, the cam angle sensor 15 does not generate a signal to identify a particular cylinder, whereby the fuel, the ignition, and so on are subjected to a sequential control based on information of the above signal.
In FIG. 6, numerical reference 100 designates a difference between a raise of a signal from the crank angle sensor and a drop of a signal from the cam angle sensor. By this difference, an angle of cam shaft, i.e. valve timing, with respect to the crank shaft is detected. The ECU 17 operates a target valve timing in response to a current running condition based on various sensor outputs, and conducts a feedback control based on a deflection between the target valve timing and the detected actual valve timing in order to control the oil control valve 16 so that the actual valve timing conforms to the target valve timing.
However, the conventional device has problems that valve timing is not controlled and cylinders are not identified in case that a cam angle sensor, by an output from which the cylinders are identified and variable valve timing is controlled, is troubled, whereby a sequential control of a fuel and ignition is impossible and the fuel and the ignition are not controlled in conformity with a running condition of the engine.
Further, in the conventional device, there are problems that actual valve timing is not detected for a predetermined cylinder and a performance of controlling valve timing is not improved because an output from the cam angle sensor is not generated for the predetermined cylinder.